Outline the Gaia hypothesis as a model of the global ecosystem.

Describe the similarities and differences between the terms sustainable yield and sustainable development.

Discuss the relationship between the economic development of countries and the sustainability of their food production.

Please note: although "quality of expression" marking is no longer used in exams, this question from a past syllabus may still be useful for student practice. While Gaia is still relevant to the current programme, it is no longer compulsory syllabus content.

Gaia hypothesis views Earth as a self-regulating system/homeostatic system/living organism;
…maintaining life-supporting conditions/equilibrium;
…through negative feedback mechanisms;
…eg where any changes in global temperature/ocean salinity/O₂ concentration stimulate mechanisms to inhibit/reverse that change;
living organisms interact with non-living elements to form habitable conditions on Earth / it proposes that the evolution of life on earth stabilised global temperatures/atmospheric composition/ocean salinity making the planet more habitable;
eg “Daisy World” where high temperatures promote growth of more reflective daisies;
humans are part of the living system, do not dominate it or have any intrinsic right of exploitation / but may contribute to positive feedback mechanisms destabilising equilibrium in the short term. 

[4 max]

Definitions (2 max):
Sustainable yield (SY) may be calculated as the rate of increase in natural capital,that is, that which can be exploited without depleting the original stock or its potential for replenishment / correct formula;

Sustainable development - “development that meets current needs without compromising the ability of future generations to meet their own needs.”;

Similarities:
both refer to exploiting the environment in a manner that does not reduce the potential for future exploitation / does not deplete the original stock;
both refer to living within the natural income of a system / living on the interest of natural capital;
both will maintain an equilibrium within the system;
both rely upon natural productivity/goods/renewable resources/natural capital;
both are economic (rather than ecological) terms;

Differences:
sustainable yield refers to a given resource but sustainable development refers to many resources/human activities;
sustainable yield is usually only applied to goods/renewable natural capital whereas sustainable development includes services/assimilation of wastes/intrinsic values;
sustainable yield is usually evaluated on an annual/seasonal basis whereas sustainable development is evaluated over an indefinite period;
sustainable yield may be estimated simply as the annual gain in biomass or energy through growth and recruitment whereas sustainable development may be quantified by ecological footprint;
there is considerable debate over what constitutes sustainable development whereas sustainable yield is a clear mathematical formula;
different value systems/political agendas/ideologies may have varying approaches to sustainable development whereas there can be only scientific debate over reliability and statistical rigor of sustainable yield (evaluate its limitations). 

Award [4 max] if only similarities, or only differences, are given.
There is always difficulty in fairly crediting “differences” in responses that just give descriptions of each of the two items being contrasted. Credit for “differences” should not be given for simple descriptive statements regarding one item, UNLESS there is a clear/explicit point of contrast being made with the other item. This may be successfully done through “whereas/however” statements, a comparative table, directly paired statements etc.
A dot annotations should be added to the first part of the difference and then the tick annotation when the difference is made.

[6 max]

Please note: although "quality of expression" marking is no longer used in exams, this question from a past syllabus may still be useful for student practice.

MEDCs may be more sustainable because…
they may be more able to afford more sustainable technology/practice (eg hydroponics/organic farming/biological pest control);
may be more environmentally aware due to greater media/communication technology (and so adopt more sustainable farming methods);

MEDCs may be more unsustainable because…
they can afford to import a large proportion of their food supply / incur high food mileage which is unsustainable;
industries may exploit LEDCs where restrictions on unsustainable practices/technologies (eg pesticides) are more lax;
may tend to favour meat-rich diets/eating at higher trophic levels that are less sustainable;
they may over-produce and generate considerable food waste for economic reasons/quotas which reduces sustainability;
they employ commercial intensive farming techniques that impose unsustainable impacts/pressures on soils/water;

LEDCs may be more sustainable because…
may be unable to afford commercial farming technology that tends to be less sustainable;
are more likely to have hunter-gatherer practises / rely on subsistence farming which may be more sustainable;
may tend to have strong cultural/historical/spiritual links with the environment and so put high value on sustainability/environmental protection;

LEDCs may be more unsustainable because…
may depend on exporting food products and so invest in less sustainable farming technology/practices / cash crops are grown rather than food crops on productive land, these are often less sustainable monocrops;
tend to have higher population growth rates leading to unsustainable/rapid increases in food production / leading to unsustainable/intensive production systems/use of marginal land to meet growing demand;
practice slash and burn as a cheap strategy/due to population growth but this is unsustainable in the long term. 

Award [7 max] for marking points above, and [1 max] for an explicit and valid conclusion that is justified by points raised.

Note to examiners: An isolated statement eg “Increased economic development leads to reduced sustainability” or an unjustified opinion eg “I think LEDCs have less sustainable farming systems” should not be considered as a valid conclusion.

The conclusion must be supported/justified by points raised.

eg historically, economic development has generally led to reduced sustainability, but recently this is beginning to change in some MEDCs;
low economic growth and reduced individual needs lead to sustainable food production system, however rapid population growth results in most LEDCs to revert to unsustainable practices as they try to increase food productivity. 

Alternative points of equivalent validity, significance and relevance to those given, should be credited.

[8 max]

Expression of ideas [2 max]

Generally, the candidates knew what the Gaia hypothesis was and could link it to the global ecosystem. Gaining all four marks was more difficult and many students repeated their initial comments.

Most candidates defined the two terms before trying to describe the similarities and differences. Many gained a similarity mark from mentioning maintaining equilibrium or both relying on natural capital. The most common difference was how sustainable development looked at services as well as goods.

The candidates struggled with the discussion aspect of the question and also with the relationship between the two aspects of economic development and sustainable food production. Instead they often described and explained how economic development could help produce food. As a result, the sustainability element was hardly mentioned in this approach to the answer. Even those candidates who successfully answered the question often missed out a conclusion.